Down-regulation of NF-κB protein levels in activated human lymphocytes by 1,25-dihydroxyvitamin D_3

摘要

The effect of 1,25-dihydroxyvitamin D_3 [1,25(OH)_2D_3], a steroid hormone with immunomodulating properties, on nuclear factor κB (NF-κB) proteins was examined in in vitro activated normal human lymphocytes by Western blot analysis. Over a 72-hr period of activation, the expression of the 50-kDa NF-κB, p50, and its precursor, p105, was increased progressively. When cells were activated in the presence of 1,25(OH)_2D_3, the levels of the mature protein as well as its precursor were decreased. The effect of the hormone on the levels of p50 was demonstrable in the cytosolic and nuclear compartments; it required between 4 and 8 hr and was specific, as 25-hydroxyvitamin D_3 and 24,25-dihydroxyvita-min D_3 were ineffective. Besides p50, 1,25(OH)_2D_3 decreased the levels of another NF-κB protein, namely c-rel. In addition, 1,25(OH)_2D_3 decreased the abundance of a specific DNA-protein complex formed upon incubation of nuclear extracts from activated lymphocytes with a labeled NF-κB DNA binding motif. Further, 1,25(OH)_2D_3 inhibited the transcriptional activity of NF-κB in Jurkat cells transiently transfected with a construct containing four tandem repeats of the NF-κB binding sequence of the immunoglobulin κ light chain gene linked to the chloramphenicol acetyltransferase reporter gene. These observations demonstrate directly that there is de novo synthesis of NF-κB during human lymphocyte activation and suggest that this process is hormonally regulated.